Free Astronomy Magazine July-August 2015

SPACE CHRONICLES T his image shows the sky around the star 51 Pegasi in the northern constel- lation of Pegasus (The Winged Horse). In 1995 the first exo- planet to be disco- vered was detected orbiting this star. Twenty years later this object was also the first exoplanet to be be directly de- tected spectroscopi- cally in visible light. This image was creat- ed from photographic material forming part of the Digitized Sky Survey 2. [ESO/Digi- tized Sky Survey 2] Jorge Martins explains: “This type of detection technique is of great scientific importance, as it allows us to measure the planet’s real mass and orbital inclination, which is es- sential to more fully understand the system. It also allows us to estimate the planet’s reflectivity, or albedo, which can be used to infer the com- position of both the planet’s surface and atmosphere.” 51 Pegasi b was found to have a mass about half that of Jupiter’s and an orbit with an inclination of about nine degrees to the direction to the Earth. This means that the planet’s orbit is close to being edge on as seen from Earth, although this is not close enough for transits to take place. The planet also seems to be larger than Jupiter in diameter and to be highly reflective. These n are typical properties for a hot Jupiter that is very close to its parent star and exposed to in- tense starlight. HARPS was essential to the team’s work, but the fact that the result was obtained using the ESO 3.6-metre tele- scope, which has a limi- ted range of appli- cation with this tech- nique, is exciting news for astronomers. Exist- ing equipment like this will be surpassed by much more advanced instruments on larger telescopes, such as ESO’s Very Large Tele- scope and the future European Ex- tremely Large Telescope. "We are now eagerly awaiting first light of the ESPRESSO spectrograph on the VLT so that we can do more detailed studies of this and other planetary systems,” concludes Nuno Santos, of the IA and Universidade do Porto.